Absorbent non-stick pads employed as the absorbent components in high quality adhesive bandages preferably include an oriented apertured web laminated to a nonwoven absorbent material. In one prior art structure the oriented apertured web is a high density polyethylene web sold under the trademark DELNET by Applied Extrusion Technologies, Inc. of Peabody, Mass. 01960, and the nonwoven absorbent material is a needle-punched web including a blend of polypropylene and rayon fibers. In this prior art structure the DELNET web has anti-stick properties relative to body wounds to be covered, and the nonwoven absorbent material has a weight of approximately 3.8 oz./yd.sup.2. These two components are heat sealed together in a bonding nip under high pressure to insure that the components are effectively bonded together and to constrain the oriented aperture web against shrinking under the temperature conditions required to effect the bonding operation.
While the above described prior art structure has functioned in a satisfactory manor in bandage applications, that structure is undesirably expensive to fabricate, particularly because of the relatively high cost of the needle-punched nonwoven absorbent component of the pad. Moreover, the high pressure required at the bonding nip to effect bonding of the nonwoven absorbent component to the oriented aperture web, while controlling, or preventing, shrinkage of the oriented web, results in the formation of an absorbent pad that has an excessively high fiber density and little entrapped air. This undesirably limits the absorbent capacity of the pad. Moreover, the required use of a high bonding pressure makes the prior art process somewhat difficult to control.
Prior art pads of the type described above generally have a thickness of 40 mils, and when incorporated into a bandage by compression generally have a thickness of approximately 35 mils., with the overall thickness of the bandage being 50 mils.
It also should be noted that nonwoven single and multi-layer constructions employing bi-component filaments and/or fibers have been disclosed in the prior art, as evidenced by U.S. Pat. No. 5,382,400 (Pike et al.); U.S. Pat. No. 5,082,720 (Hayes); U.S. Pat. No. 4,883,707 (Newkirk) U.S. Pat. No. 5,246,772 (Manning) U.S. Pat. No. 4,732,809 (Harris, Jr. et al.). However, none of these prior art patents discloses or suggests the formation of laminated constructions including a fluid-pervious, oriented plastic substrate bonded to a nonwoven absorbent web including bi-component fibers in it, as in the present invention.
The Pike et al. '400 patent discloses the formation of single and multi-layer nonwoven webs employing helically crimped bi-component filaments. The disclosed bi-component filaments can include a polypropylene core surrounded by a polyethylene sheath. In the disclosed multi-layer constructions each layer includes bi-component filaments in it, with the degree of crimp of the bi-component filaments in one layer being different from the degree of crimp of the bi-component filaments in the other layer. (column 10, line 36 et. seq.).
The Hayes '720 patent discloses melt-bondable, bi-component fibers and nonwoven webs made from such fibers. The bi-component fibers include a core having an at least partially crystalline polymer and a sheath including a compatible blend of polymers including at least one amorphous polymer and at least one partially crystalline polymer. The polymer sheath melts at a temperature lower than that of the polymer core.
The Newkirk '707 patent discloses a laminate of two carded webs having bi-component fibers in them. Bonding of the fibers in each web and between the webs is achieved by thru-air bonding with heated air to thereby activate the sheath layer of the bi-component fibers. The laminated carded web is described for use as coverstock for disposable diapers, sanitary napkins, and the like.
The Manning '772 patent discloses a laminate including an airlaid, nonwoven pulp web layer on opposed sides of, and reinforced by a wetlaid bi-component web layer. The bi-component web layer includes bi-component fibers wherein the sheath component has a lower melting point than the core component. Bonding of the layers is effected through the sheath of the bi-component fibers, and also preferably by utilizing an additional latex adhesive.
The Harris Jr. et al. '809 patent discloses the use of bi-component filaments or staple fibers in forming nonwoven webs. The disclosure is directed to a bi-component filament including a polyester core and another latently adhesive component (e.g., the sheath) having a melting point below that of the core.
The prior art also discloses other multi-layer constructions intended to obviate the problem of shrinkage during the bonding of the various layers to each other. For example, note U.S. Pat. No. 4,348,445, to Craig, wherein a laminate is disclosed that includes an unoriented film formed of a propylene/1-butene copolymer bonded to a netting layer including oriented fibers. This patent discloses laminates wherein two of such film layers are bonded to a central netting layer, and wherein two netting layers are bonded to a central film layer. The selection of materials allegedly prevents shrinkage or distortion of the oriented netting layer(s) during the bonding of the multiple layers into a laminate construction.
The prior art also includes numerous additional disclosures of multi-layer and/or multi-fiber fabrics wherein one or more of the fibers/layers is a thermoplastic material that functions as a bonding agent in the fabric. For example, note the disclosures in U.S. Pat. No. 5,362,546 (Boulanger); U.S. Pat. No. 4,545,372 (Lauritzen) U.S. Pat. No. 4,041,203 (Brock et al.) U.S. Pat. No. 3,846,205 (Yazawa); U.S. Pat. No. 4,657,802 (Morman); U.S. Pat. No. 4,726,976 (Karami et al.); U.S. Pat. No. 4,214,582 (Patel); U.S. Pat. No. 3,285,245 (Eldredge et al.) and U.S. Pat. No. 5,114,787 (Chapline et al.). However, none of these latter patents discloses or suggests the formation of laminated constructions including a fluid-pervious, oriented plastic substrate bonded to a nonwoven absorbent web including bi-component fibers in it, as in the present invention.
The Boulanger '546 patent discloses a nonwoven fabric intended for use as a facing layer on a molded fibrous mat. The nonwoven fabric is a laminated structure including a first layer having bond-forming fibers (e.g., low melt polyester, polyethylene and polyamide) mixed with and bonded to filler fibers (e.g., rayon, acrylic, cotton, polyester and polypropylene fibers) and a second layer including fibers (e.g., high melting point polyester fibers) that will not melt at the fusion temperature of the bond-forming fibers of the first layer. These two layers are intermingled together in a process that forms the nonwoven fabric into the general configuration shown in FIG. 5 of the '546 patent.
The Lauritzen '372 patent discloses an adhesive bandage construction employing a nonwoven fabric including a mixture of absorbent fibers (e.g., rayon staple fibers, cotton fibers, short length natural cellulose fibers such as wood pulp fibers and cotton linters, and mixtures thereof) and conjugate fibers (e.g., bi-component fibers including a polyester core and a polyethylene sheath). In one embodiment a light weight veneer of heat-fusible fibers is provided on each surface of the nonwoven fabric and will bond to each other and to the adjacent nonwoven fabric at the temperatures employed to activate the bonding properties of the conjugate fibers of the nonwoven fabric.
The Brock et al. '203 patent discloses a nonwoven fabric laminate including a top layer in the form of a mat including thermoplastic microfibers and a bottom layer in the form of a web of substantially continuous and randomly deposited, molecularly oriented filaments. These layers can be secured to each other by the application of heat and pressure at intermittent areas along the fabric, or alternatively by using an independently applied adhesive or by the mechanical interlocking of the fibers, such as be needling techniques well know in the art.
The Yazawa '205 patent discloses a flexible, gas-permeable nonwoven material including a web of split fibers secured with a shaped binder (e.g., a perforated film) that preferably is of the same polymer as the split fiber but that has a lower melting point than the split fiber by virtue of being unoriented.
The Mormon '802 patent discloses a nonwoven elastic substrate including an elastic web (e.g., melt blown fibrous nonwoven elastic web or aperture web of an elastic film) that is heat bonded to a fibrous nonwoven gatherable web while the elastic web is maintained in a stretched condition. Thereafter the stretching or biasing force is removed from the composite nonwoven elastic substrate, resulting in the nonwoven elastic web returning to its unstretched, relaxed condition with the nonwoven gatherable web being gathered.
The Karami et al. '976 patent discloses a composite substrate usable as a coversheet on disposable articles such as disposable diapers, sanitary napkins, disposable bed pads, nursing pads, finger dressings and incontinent diapers, or the like. The substrate includes a thermoplastic film secured to and between fibrous webs through a heat embossing operation that also forms apertures in the thermoplastic film.
The Patel '582 patent discloses a multi-layer surgical dressing employing a multi-layer nonwoven fabric including outer surface layers employing heat-sensitive fibers such as polypropylene, nylon, or textile-length polyester fibers, and an interior layer employing polyester binder fibers that soften at a temperature lower than the fibers in the outer surface layers. This patent also discloses the bonding of a gauze fabric to the nonwoven fabric by melting heat sensitive fibers adjacent the gauze fabric.
The Eldredge et al. '245 patent discloses an absorbent wound dressing including a multi-layer pad formed in a continuous process, wherein the non-stick top, or release, layer of polypropylene fibers is heated to melt the fibers and aid in securing the top layer to the underlying absorbent fibers (e.g., cellulose acetate fibers).
The Chaplin et al. '787 patent discloses a multi-layer nonwoven web including at least one layer of a self-bonded fibrous nonwoven web bonded to at least one layer of a carded web. As disclosed the fibrous nonwoven web can include thermoplastic filaments comprising a variety of different polymers, e.g., polypropylene, high density polyethylene, low density polyethylene, linear low density polyethylene, polyamides, polyester, blends of polypropylene and linear low density polyethylene. The carded web can include a variety of staple fibers, e.g., cotton, polypropylene, blends of polypropylene and polybutenes and blends of polypropylene and linear low density polyethylene.
The disclosures of all of the patents identified in this Background Art section are incorporated herein by reference.
Based on the state of the prior art applicant has determined that the need exists for an absorbent, non-stick laminate that is less expensive to fabricate than prior art structures, that can be easily fabricated without the use of excessively high pressures required in prior art processes to effect bonding and to control shrinkage, and that has improved absorbent properties. It is to such a construction that the present invention is directed.